What if Star Trek-style mind melding was more than a science fiction concept?

The brain-to-brain interface is a challenge right on the limit of our understanding of neuroscience but scientists are working to bridge this gap, some funded by the Defense Advanced Research Projects Agency (DARPA), the secretive research wing of the US military. The task is, put simply, to use science to make a telepathy machine. But how on earth would you do that?

The research wing of the US Department of Defense, DARPA is developing something called Next-Generation Nonsurgical Neurotechnology, or N3. In short, it wants wearable, “man-portable” brain devices that help soldiers do their job better – without surgery.

DARPA has bestowed US$26 million (about AUD34 million) on a research program led by Jacob Robinson, a neuroengineer and associate professor at Rice University in Houston, Texas. As you can imagine, Robinson had to write a detailed proposal to secure the DARPA funding and it was during that intense period he received something auspicious in the post. It was a birthday present from his brother – the video game Call of Duty: Modern Warfare. The game was a welcome distraction and Robinson fired it up pronto but, within a few minutes, his character was dead. Fortunately, though, the game has a reanimation feature where you come back to life with some extra cool tech.

“What this neurotechnology allows you to do is to see everything that your team can see,” says Robinson. “So if your teammate sees a bad guy behind a wall, you can see that bad guy behind the wall. And so everybody shares that same sensory experience to give you a complete view of the battlefield.” It was, says Robinson, a coincidence, because that feature was spookily close to what the DARPA N3 program hopes to produce.

Of growing importance in modern warfare is the unmanned aerial combat vehicle, or combat drone. Drone operators sit at a computer station and need to process reams of information. They must identify targets and plan flight paths, deploy missiles and have a clear understanding of the location of personnel of all stripes. Information comes from systems onboard the drone and from soldiers in the field, some of it verbally through headphones and some visually on the monitor. There is a lot going on. What if the process could be simplified? What if, just like Call of Duty, the drone operator could receive a stream of “percepts” directly from other brains that convey all the required data about an enemy?

In 2019 Robinson put the collective shoulder of his team to the wheel. Their first challenge was to “read” a brain with sufficient resolution to capture the richness of a thought – say, the presence of a tank. So, what happens in a soldier’s brain when they see a tank? The action happens in the vision centre of the occipital cortex, which has a peculiar trait called retinotopy. Let’s say you see the letter “M” out there in the world. It actually gets mapped as an upside down “M” on the visual cortex. Literally. If you do a functional MRI scan the active brain cells trace out the letter so faithfully it looks like the occipital cortex has been branded with an “M”. See a tank and it will be reproduced similarly on the visual canvas of the brain. But there’s a problem: to read a complex percept like a tank moving at speed, you need to measure the dynamic firing of many individual neurons over a short time span. To do that, Robinson needed much higher resolution than the MRI could offer.

The team turned its sights to something called a GEVI, or genetically encoded voltage indicator. These are fluorescent proteins that, when inside a neuron, detect the electrical changes that happen when it fires. The proteins respond by changing colour. Get GEVIs into a bunch of cells in the visual cortex and you could find out which ones were firing and what the soldier was seeing, with resolution at the level of individual neurons. But how, precisely, would you get a GEVI into a soldier’s brain cell?

In mice it’s possible to attach the GEVI genes to a virus – a relative of the adenovirus that causes the common cold – which infects the cell and co-opts its machinery to make the GEVIs. But you don’t want a scattergun result; you want your GEVIs confined to the visual cortex. The solution is to inject your genetic payload into the blood with a stream of tiny air bubbles. Then you direct a beam of ultrasound onto the bubbles and something special happens.

“When that focused ultrasound interacts with the microbubbles, the bubbles cavitate and that opens up the blood brain barrier. So those viruses that are in the blood can then escape the blood brain barrier only in that specific spot,” says Robinson.

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